A non-volatile memory device having an array of non-volatile memory cells is well known in the art. Typically, a device also has a number of non-volatile reference memory cells provided with the array. In addition, typically, multiple comparators are provided with the array of non-volatile memory cells to provide for parallel reading. Each comparator is associated with a group of the non-volatile memory cells in the army. Further, each comparator is connected to one of the reference cells, and uses the signal from the reference cell and compares it to the associated group of memory cells. Finally, in the prior art, all of the comparators are either all connected to a single non-volatile memory reference cell or all of the comparators are connected to a number of non-volatile memory reference cells wherein all of the non-volatile memory reference cells are set to the same targeted signal value.
Because of process variations, and other anomalies, the I-V (current-voltage) characteristics of individual transistors in the comparators will have different offsets and cause the comparators to have different “effective reference levels”. This results in the operating window being larger than otherwise necessary to take into account such large difference in the reference levels.